The invention relates to a piston pump which is intended for use as a return feed pump for a slip-controlled vehicle brake system.
Such piston pumps are known per se. For example, see the piston pump disclosed in German Patent Disclosure DE 40 27 794 A1. This known piston pump has a pump housing, in which a piston that can be driven to execute a reciprocating stroke motion is axially displaceably received. For fluid admission, the piston of the known piston pump has an axial bore, which extends to approximately the middle of the piston and is intersected by a transverse bore. At an orifice of the axial bore at one face end of the piston, a valve seat made by metal cutting machining is provided for a check valve, which in the known piston pump forms an inlet valve. The piston is a part made by metal-cutting machining in the form of drilling and turning on a lathe. The piston is complicated and expensive to make.
The piston of the piston pump of the invention is a deformed part, which is made for instance by upsetting or extrusion. In the same operation as the production of the piston, a flow conduit is also made without metal cutting, for instance in the form of an axial hole for admitting or discharging fluid. A valve seat of a check valve, which may form an inlet or outlet valve of the piston pump of the invention, is also formed onto the piston in the same operation with the production of the piston. The valve seat can be formed on the piston on a face end of the piston at an orifice of the flow conduit, for instance, or on an annular shoulder inside the flow conduit. Making the valve seat by deformation without metal cutting has the advantage of hardening the material, and the dimensional stability and strength of the material can be increased by a concluding swaging or reswaging of the valve seat. If the piston is guided by slide rings in the pump housing, remachining of the circumferential surface of the piston by fine lathing, grinding, honing or the like becomes unnecessary.
The piston pump of the invention has the advantage that its piston can be made entirely without metal-cutting machining, by deformation in a single operation or in only a few deforming steps. This makes the piston fast and economical to produce, and there is no waste of material. Remachining the piston surface or making bores, grooves or the like by metal-cutting machining, which in piston production would require additional machining steps and machining tools, also becomes unnecessary. The valve seat hardened by deformation has the further advantage of greater wear resistance and thus a longer service life.
The piston pump of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR and EHB are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR or FDR or EHB). The pump is needed in a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (FDR) and/or an electrohydraulic brake system (EHB). With the wheel slip control (ABS or ASR), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (ASR) can for instance be prevented. In a brake system serving as a steering aid (FDR), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track intended by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.